Manual transmissions have been used for a very long time in different type of motor vehicles. Since, particularly, piston driven internal combustion engines have relatively limited useful rotational speed ratios, the manual transmission is charged with the task of adapting the rotational speed ratio between the output shaft of such a drive motor and the rotational speed of the driven wheels, such that the drive motor can be operated within a desired rotational speed range. For this purpose, like the so-called continuously variable transmissions, which allow the setting of any desired transmission ratios, they are mainly used in step-by-step variable speed transmissions. These transmissions are characterized by a number of discrete gears with respectively different gear transmission ratios.
When changing a gear and also when engaging a gear speed from idle, the participating mechanical components, such as shafts and/or gear wheels, are initially slowed or accelerated to an approximately synchronous rotational velocity. For this purpose, when a clutch or driving clutch, between the drive motor and the transmission, is disengaged, the transmission is brought initially into the neutral position if a gear is previously engaged. The same as the components, which are to be brought into an active connection, are accelerated or slowed approximately to the synchronous speed.
Since the rotational speed of the transmission output is generally closely associated to the rotational velocity of the vehicle wheels, the rotational speed of the transmission input must be selected in correspondence with the rotational speed of the transmission output, taking into consideration the gear ratio of the engaged gear. While the slowing of a respective transmission shaft is generally achieved by way of brakes arranged inside or outside of the transmission, acceleration can be achieved within the transmission, via special synchronizing mechanisms, which are independent from the drive motor, but which are still quite complex.
Acceleration of transmission components of the transmission input can be achieved, however, in a particularly simple way by way of the drive motor itself. For this purpose, starting from the neutral position of the transmission, the driving clutch is engaged at least so far that a sufficiently great torque can be transmitted by the drive motor to the transmission input shaft.
The engine rotational speed is controlled such that the transmission input shaft is accelerated according to the specification. Therein, the driving clutch can be engaged in a rotationally fixed manner and the transmission input rotational speed can be set by way of the engine control of the drive motor. It is basically also possible that the engine rotational speed has a higher value than that set for the rotational speed required for transmission synchronization and that the actual synchronization of the shaft rotational speeds is carried out, via a corresponding control of the driving clutch and/or a braking mechanism. It is important here that the rotational speed of the drive motor is at least correspondingly high to increase the rotational speed of the transmission parts by way of synchronization and that the necessary kinetic energy is made available to the latter.
In at least partially unsynchronized transmissions such as these, it is possible that the drive motor is unable to provide the required rotational speed and/or sufficient torque for synchronization of the transmission to allow the desired gear to be engaged. The possible reasons for this are many and do not need to be further discussed at this point.
In a case such as this, engagement of the desired gear is not possible, because the corresponding transmission parts cannot be accelerated. With this, the transmission remains in a neutral position or it is incumbent upon a driver to select a gear, which can be engaged, via slowing of the transmission parts, to be synchronized, when this unexpected situation arises.
At this point, since the transmission input is separated from the drive motor, its rotational speed diminishes very quickly and only a short time span is left for the driver to attempt a shift such as this. From the driver's point of view, concerning a motor vehicle with an automatically shifting transmission, the transmission engages therein, without detectable reason, into the neutral position and the drive motor runs irregularly with a very low rotational speed or even stops. In such an operation case, a driver with a manually shiftable transmission experiences that when a gear change is required, the transmission shifts into idle and the engine displays the already described behavior.
In this situation, an average driver will hardly be able to identify and manually select a gear into which he can still shift so that when this happens the vehicle can normally coast with the transmission in the neutral position.
In specific malfunctions of the drive motor, it would indeed be possible to at least still drive for a short distance with the vehicle and reach the nearest highway exit ramp, a shop or at least get out of a dangerous situation, such as a highway entry ramp, even if the transmission would remain in the neutral position during the change of gear to a lower gear, because of the unavailable rotational speed increase or the insufficient available torque of the drive motor.
In addition, there are situations in which the defective state of the drive motor is present only for a short time so that driving can be initially continued, when it is possible to support the drive motor for a specific time by supplying kinetic energy from the vehicle wheels, via the manual transmission and the clutch.
Based on these circumstances, it is an object of the invention to present a method for controlling an at least partially unsynchronized manual transmission, which also prevents unintentionally holding the transmission in the neutral position, when the drive motor is unable to provide the rotational speed available with a sufficient torque, which is required for synchronization of the transmission.